Laser ultrasound technique for material characterization of thermal sprayed nickel aluminum coatings in elevated temperature environment

Abstract

Thermal spraying processing usually use nickel-aluminum alloy system as major powder due to its strong adhesion to substrates. The contents of powder material and the processing parameters used in the spraying process cause material properties of coating exhibiting a wide variation. It is difficult to investigate mechanical properties of coating layer in nondestructive way. This research focuses on characterizing mechanical properties of thermal spraying coatings at high temperature environment up to 295° C in nondestructive way. A laser ultrasound technique (LUT) is used for the measurements of dispersion spectra of guided waves. Theoretical model for surface waves propagating along a multi-layered structure with coating and substrate is used to model the sprayed coatings. An inversion algorithm based on Shuffled Complex Evolution (SCE-UA) is used to extract mechanical properties from the measured dispersion spectra cooperating with theoretical model. In the results, surface wave dispersion spectra are measured for three different thickness coatings at different temperature environment. The difference thickness of coatings and temperature environment are reacted to dispersion spectrum of guided waves. It also related to mechanical properties of coating in theoretical model. This method is potentially useful to characterize the mechanical properties of thermal spraying coating in a nondestructive way.